They are calling you 'Big guy' because you are TALL, dude!! It's a 'term of endearment' and means they like you! Some are probably jealous, and want to be as tall as you!!Just smile, and make up some nicknames for them!! Play along! Don't take it as offensive, OK? I doubt that they are meaning to hurt you! :)

I'm 6'1", mostly Scandinavian, and maybe 250. In college, I worked with a smaller guy, from Guadalajara, and when we first met, he looked me up and down, and then again. In decent English, he asked "So you is a Viking, or what?" All of the others (mostly Latinos, Mexican, Salvadorian, Guatemalan, etc) called me 'Viking' from that day on! I ended up becoming their shop steward, in the union, because they all seemed to hate each other, but they all trusted me. Go figure!!